Accessing Data Space Storage

To gain access to the data space, the program calls the DMSSPLA (Establish Address Space Addressability) routine, specifying the ASIT of the data space, which was returned on the Create or Query call. DMSSPLA adds an entry to the access list and returns an access list entry token (ALET). The access list entry (ALE) identifies the newly created data space and the ALET selects the entry.

The access list referenced in this discussion is associated with the virtual machine's primary address space and is also referred to as the host access list. This access list is equivalent to the primary address space access list (PASN-AL) of MVS/ESA.

Figure 1 shows the relationship of an XC virtual machine's address space components. Each CMS user virtual machine has a primary address space where CMS and application programs execute. Associated with a primary address space is the access list that contains entries to data spaces, in this case DataSpaceX and DataSpaceY. When a data space entry is placed on the access list, an ALET is obtained from the system. The ALET indicates to the system which data space to address when making storage references. The application places this ALET in the access register associated with the general register containing an operand whose value is to be fetched from the data space.
Figure 1. Data Space Addressability
                User1     (XC)
   +----------------+          DataSpaceX          DataSpaceY
   |                |    +-->+------------+   +->+------------+
   | +----------    |    |   |            |   |  |            |
   | |PGM1          |    |   |            |   |  |            |
   | | ...          |    |   |            |   |  |            |
   | | ...          |    |   |            |   |  |            |
   | |              |    |   |            |   |  |            |
   | | ALETX  DC  F |    |   |            |   |  |            |
   | | ALETY  DC  F |    |   |            |   |  |            |
   |                |    |   |            |   |  |            |
   |                |    |   |            |   |  |            |
   |                |    |   |            |   |  |            |
   |                |    |   |            |   |  |            |
   |                |    |   |            |   |  |            |
   |                |    |   +------------+   |  +------------+
   |                |    |                    |
+--+--+------------++----+--------------------+------------------+
|     | DataSpaceX +-----+                    |                  |
|     +------------+                          |                  |
|     | DataSpaceY +--------------------------+------------------+  
|     +------------+                                             |
|      Access List                                               |
|CP                                                              |
+----------------------------------------------------------------+